The invention concerns a two beam alternating light colorimeter consisting of an illumination lens system and a control device, which, with the help of two stationary reflecting mirrors, deflects the measuring beam which is produced by a light source in alternating fashion through a first measuring cell and following this through a second measuring cell onto a common light sensitive element or cell. A measuring and evaluating circuit is also provided which is connected with the light sensitive element.
The advantage of a two beam alternating light colorimeter of this sort with respect to the other known one beam and two beam colorimeters consists in the use of a single radiation deflector in the form of a light sensitive element for the measuring and comparing beam signal. By means of the use of two measuring cells conducting the object liquid wherein one has a comparatively great thickness and the other displays only a half thickness, it becomes possible to compensate the measured value falsifications which are brought about by means of dirt accumulations of the cell windows. By means of the use of measuring cells of the same layer thickness wherein one contains the object liquid and the other contains a reactive fluid, it becomes possible to compensate the reactive components. By means of processing of the electrical measuring signals according to the photometric law of absorption, it becomes possible to determine the concentration of the components which are to be measured in the object liquid. The known two beam, alternating light colorimeters possess a control device which guides the measuring beam produced by an illumination lens system as an alternating pulse first through a first measuring cell and following this through a second measuring cell. For this, usually a rotary shutter (chopper disc) is used, where, by means of a mirror system, the measuring beam which was produced by the illumination lens system is directed to the cell windows of the two measuring cells. The measuring signal which was provided by the single photoresistor or respectively, light sensitive element is conveyed to a measuring circuit where the output voltage of the measuring circuit is a measurement for the concentration of the object liquid.
A two beam chopped light colorimeter of this kind became known through German OS 2,536,188, incorporated herein by reference, in the case of which in the path of the measuring beam which is coming from the illumination lens system, a semitransparent mirror is arranged at an angle of 45.degree.. In this way, the portion of the measuring beam which is reflected by the semitransparent mirror is deflected by 90.degree. relative to the portion of the measuring beam which is allowed to pass through. By means of a respective additional mirror in the optical path of both partial measuring beams, these are deflected to the light sensitive elements. Since both partial beams constantly act upon the light sensitive element, a rotating shutter is provided which brings the two beams into a chopped effect. Also, synchronizing switches must be provided which must be controlled in dependence upon the rotating shutter disc. With the help of these synchronizing switches, the output signals of the measuring beams are provided to corresponding analog memories from which they are supplied for further evaluation.
This known two beam alternating colorimeter requires a significant expenditure for the mechanical arrangement and electronics on the one hand because of the rotating shutter and on the other hand because of the storage of both signals.